Amplifier



AMPLIFIER Filed March 5, 192B 4 Sheets-Sheet l BA'mvz-zngons y l 4:3 p d? 5 M22.

. 2 A'II'TORNEY May 19, 1931. R. DAVIS ET AL 1,806,281,

AMPLIFIER Filed March 3, 1928 4 Sheets-Sheet 2 ATTORNEY meat! May 19, 1931 UNITED STATES PATENT, OFFICE ROBERT L. DAVIS, OF PITTSBURGH, PENNSYLVANIA, AND DONALD G. LITTLE, OF LONG MEADOW, MASSACHUSETTS, ASSIGNORS TO WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA AMPLIFIER Application filed March 8, 1928. Serial No. 258,778.

Our invention relates broadly to amplifiers, and it has particular relation to amplifiers of the balanced, or push-pull, type designed to handle large amounts of power at extremely high radio-frequencies.

When economy of space is necessary in amplifiers handling power much in excess of one kilowatt, thermionic tubes having water-cooled anodes must be used. The

water-jackets and the water-pipes connected thereto have a large capacity to ground and, since these jackets and pipes must be electrically included in the tuned output circuit of the amplifier, such capacity has heretofore prevented the building of a successful radio transmitter capable of handling many kilowatts of power at high frequencies.

In addition, the ground-capacity of the water-jackets and associated piping has previously greatly hampered the satisfactory neutralizing of amplifier stages against parasitic oscillations, by reason of the fact that the said capacity was, of itself, more than that required by the neutralizing circuit.

It is, accordingly, an object of our invention to provide an improved construction and arrangement of the various elements constituting an amplifier-stage of the balanced type arranged to handle large amounts of power at hi h frequencies.

Another 0 ject of our invention is to so improve the construction and arrangement of an amplifier stage of the aforementioned type that the neutralization thereof against parasitic oscillations may be positively accomplished with minimum adjustment.

Another object of our invention is to provide, ina neutralized amplifier comprising a plurality of high-power, water-cooled thermionic tubes, instruinentalities whereby the neutralization of the amplifier against para sitic oscillations shall not be disturbed by changes in the tuning of the output-circuit thereof.

Another object of our invention is to so arrange the various elements constituting a high-power amplifier that connections therebetween shall be minimized in length.

Another object of our invention is to so arlll range: the various elements constituting .a

high-power amplifier that the device utilized for tuning the output circuit thereof may be maintained at substantially ground potential insofar as radio frequencies are concerned.

In a preferred commercial embodiment of our invention, we attain the aforementioned objects by rigidly supporting the Water-jackets for each of the several groups of tubes required for a push-pull, or balanced amplifier, between two vertically-positioned, semi-cylindrical, plates to which the said water-jackets are conductively connected. The groups of tubes, and their associated plates, are symmetrically positioned with respect to a vertical, rotatable shaft on which are mounted two semi-cylindrical plates similar to those associated with the tubes, the plates carried by the shaft and two of the plates associated with the tubes being utilized as a tuning condenser. The output inductor is constituted by a metallic pipe which con veys cooling water to the water-jackets, and which is conductively connected thereto.

Each of the remaining semi-cylindrical plates associated with the several groups of tubes is provided with a cooperating plate similar in character thereto, the said cooperating plates being mounted on vertical, rotatable shafts and, together with the plates connected to the tubes, constituting a plurality I of neutralizing condensers.

The vertical shafts on which the rotors of the tuning and neutralizing condensers are mounted are rovided with adjusting devices which exten therefrom through an instrument panel located well outside of the electro-static field, thusv minimizing the effect 1 of the capacity to ground of the attendants body during the operations of tuning and neutralizing.

As will be explained more fully later, the central shaft carrying the rotor of the tuning condenser may be maintained at substantially ground potential in so far as radio-frequency is concerned, as may also be the central point on the tuning inductor, thus minimizing the dan er to the attendant during the o oration o tuning the amplifier.

Un esirable ground-capacity effects from the tuning and neutralizing condenser-plates are minimized by mounting them vertically, and by symmetrically arranging the said plates with reference to a point that is maintalned at ground potential, the process of neutralizing the amplifier against parasitic oscillations is simplified.

By virtue of the aforementioned arrangenent of tuning and neutralizing condensers in close proximity to the groups of tubes, we

are enabled to reduce 'the'length, of'connecting leads far below that'ever before attained in similar apparatus. In addition, the several condensers, being of massive construction; are .much more rlg d than has heretofore been thought possible, which -enables the amplifier to function with extreme stability of outpu amplitude.

We also find it advantageous to interpose a grounded metallic shield between the rotor of the tuning condenser and the output inductor, in order that the inductance of the latter shall not be changed by the angular adjustment of the said rotor.

The novel features that we consider characteristic of our invention are set forth with particularity in theappended claims. The

invention, itself, however, both as to its organization'and its method of operation, together with further objects and advantages thereof, will best be understood by reference to the following description of a specific embodiment, taken in connection with the ac- "portions of the members which serve both as output inductors and as conduits for the sup- 4 ply of cooling water to the thermionic devices,

Fig. 6 is a view in perspective of certain elene'nts comprised in the amplifying unit, an CW -Figl 7 is a. diagrammatic view of the circuits and "apparatus constituting the ampli-' fying unit. r

Theapparatus illustrate in i 3 comprises a front vertical pa'n'el 1 supported by a plurality of upright members 2 which are lnterconnected by horizontal 1 bracing members 3 to form a box-likestructure. The

' panel carries" a plurality of large insulators 4, 5, 6', 7, 8, and 11, which are aflixed to the panel by bolts 12-01 analogous devices,

An insulatorlO is positioned immediately below the insulator 7 and is affixed to the panel. A metallic shelf 13 is aifixed to the insulator 7 an a similar shelf 14 is aflixed to the lower insulator 10, the two shelves extending back horizontally from the panel.

Each of the shelves 13 and 14 is provided with two openings therethrough, the several sets of openings being vertically aligned. Water-jackets 15 and 16, having enlarged upper portions 17 and 18, extend through the several pairs of aligned openings, the enlarged portions contacting with the upper shelves and serving to support the jackets in position thereon.

An insulator 19 is affixed to the panelimmediately below the insulator 5, these two insulators serving to support two similar water-jackets 20 and. 21 by means of horizontally-extending shelves 22 and 23 in the same manner that the insulators 7 and 10 support the water-jackets 15 and 16.v

A vertical curved plate 24 is aflixed to the shelves13 and 14, carried by the insulators 7 and 10, and a similarly curved plate 25 to aflixed to the shelves 22 and 23. An insulator 26 is aflixed to the panel immediately below the insulator 6, and a vertical shaft 27 is mounted for rotation inbearing devices 28 and 30 afiixedto the backwardly extending ends of the said insulators. Theshaft 27 carriesa plurality of vertical curved plates 31 and 32, similar in curvature and size tov the plates 24 and 25 carried by the water-j ackets and cooperating electrostatically therewith to constitute a variable condenser. 4 5

The lower bearing device 30 has a laterally extending ear-portion'33, in which is rotatably 'mounteda shaft 34 that carries a worth 35. The worm 35 meshes with a pinion 36 which encircles the shaft 27 and is aflixe'd thereto.

In order that the shaft 34 maybe rotated by the attendant without danger, the portion thereof extending trough the panel is insulated from the remainder by an element 38, preferably made of' micarta or equivalent material.

A curved vertical late 40 is carried by the shelves 13 and 14"d1ametrically opposite to the plate 24:, and is-electrically connected thereto through the shelves. A vertical shaft 41 is mounted for rotation in bearing devices '42 and 13 carried by the insulators Band 11, this. shaft being provided with a segmental curved. plate 4.4; which electrostatically cooperates Withjhecur'ved plate 40 to constitute a neutralizing condenser. ,The bearing 'device'43 carried by the lowerinsulator 11 'is provided with lateral extension inwhich j is rotatably mounted a shaft 45 which carries a worm .46. Th worm 46 engages a pinion 4:7 aflixed totheverticalishaftal. -The shaft v45 extends toward the panel and" is provided with an insulating'insert48.

A urved vertical plate 50 is also carried by the shelves 22. and 23 which support the water-jackets 20 and 21, diametrically opposition to the plate 25. Theplate 50 con- 'st1tutes one element of a neutralizing condenser, the other element of which is constituted by a plate 51 that is supported from a vertical shaft 52. The shaft 52 is rotatably mounted in bearing members 53 and 54 car ried by the insulators 4 and 55, respectively, and is provided with actuating devices comprising ashaft 56, a worm 57, and a pinion 58. Since that portion of the shaft 56 carrying the worm 57 is at high potential when the amplifying unit is in operation, it is insulated by an element 60 from that portion which projects through the panel.

The vertical plates 24 and are additionally supported by a horizontal shelf 61 carried by an insulator 62, which insulator is, in turn, affixed to one of the lower cross members 3 of the framework.

The plates 25 and 50 are maintained in position and supported by a similar shelf 59 carried by an insulator (not shown) analogous to the insulator 62. The two sets of water-jackets are connected electrically through two metallic pipes 63 and 64, the pipe 64 being centrally connected to a source of cooling water through a rubber hose 65. The pipe 63 has two similar hose connections 66 and 67 and serves as an outlet for the cooling water.

The several hose connections are given a length sufiicient to reduce leakage through the cooling water to a negligible value, and

they are preferably coiled around an insulating form 68 as shown in Fig. 1. The course of the cooling water is indicated by the arrows in Fig. 1, and may be traced, insofar as the water-jackets 15 and 16 are-concerned, through the pipe 64, a pipe connection 71 to the water-jacket 15, upward in the said water-jacket, downward through a connection 72, upward through the water-jacket 16, and downward through a connection 73, to discharge through the inner pipe 63 to the hose connection 66. Cooling water is also supplied to the water-jackets 20 and 21 from the pipe 64 in a similar manner, being discharged from the said jackets through a connection 74 into the pipe 63, and going therefrom to waste through the hose 67.

As illustrated in Figs. 4 and 5, the inner pipe 63 is provided with a central barrier 75, which barrier prevents admixture of the heated water from the two groups of water-jackets without interrupting the electrical continuity of the connection therebetween.-

The two groups of thermionic devices are connected in push-pull or balanced relation, as shown in Fig. 7, the elements of the ampli g unit which have already been descri ed designated by numbers, being similarly numbered in the said figure. For convenience in illustration, each group of thermionic devices is represented by a single device in Fig. 7.

Referring particularly to F 1g. 7 the thermionic devices 80 and 81 are provided with a common source 82 of filament potential, one terminal of which has a round connection 83. The grids of the devices 80 and 81 are mterconnected through an input inductor 84, tuned by a balanced condenser 79, to appropriate points on which inductor are connected leads 85 from a preceding amplifier stage. The electrical midpoint on the input inductor is connected to ground through a stopping condenser 86 and damping resistor 89. The anodes of the two devices are interconnected through an output inductor which, although shown with a plurality of turns, corresponds electrically to the two previously described plpes 63 and 64 which interconnect the groups of water-jackets. One end of a resistor 87 is connected to the electrical midpoint of the output inductor and the other end of the resistor is electrostatically connected through a stopping condenser 88 to ground. The end of the resistor 87 connected to the condenser 88 is also connected through a choke-coil 90 to a source of high potential supply (not shown) for the anodes of the devices.

. 'The amplified output is fed to' a succeedmg stage or to a radiating structure through a plurality of conductors 91 and 92. A shield 93 (indicated by dotted lines) is interposed between the tuning condenser rotor and the output inductor, in orderthat the inductance of the latter, or its capacity to ground, shall not be changed when the said rotor is adjusted. The shield 93 is shown in its preferred position in Figs. 1 and 2.

The stray capacity between the anodes of the several devices and the water-jackets and piping associated therewith, and ground, is indicated in Fig. 7 by the dotted line condensers 94 and 95. It will be noted that these capacities are efi'ectively in shunt to the output inductor 6364, and would obviously constitute a portion of the tuning capacity required.

Although the stationary elements 24-25 of the tuning condenser are shown in Fig. 7 as connected to the anodes of the devices 80 and 81 through conductors 96 and 97, respectively, no such conductors are present in the actualstructure, inasmuch as the stationary plates are substantially electrically integral with the water-jackets which support the thermionic devices and'make contact with the anodes thereof. In like manner the conductors 98 and 100 which appen in Fig. 7 as connecting the stationary members of the neutralizing condensers 40 and 50 to the anodes are not present in the actual structure, inasmuch as the said stationary plates are also practically integral electrically with the water-jackets referred to, which waterjackets are in intimate contact for at least a portion of their length with the exterior and 88, and the resistor 87 as well as other minor incidental apparatus, not shown on the drawin such as resistors, condensers and .the like. umerous other auxiliary elements of the amplifying unit, such as water-flow auges, connections, etc., have been omitted rom Figs. 1 to 6 in order that the main invention shall not be obscured.

The conductors 101 and 102, which crossconnect the movable elements 44 and 51 of the neutralizing condensers to the grids of the opposite groups of tubes, may be made of minimum length, inasmuch as the several groups of tubes are, in practice, separated only sufficiently to permit the actuation therebetween of the movable member's 31-32 of the tuning condenser.

The oscillating circuit of the amplifier comprises the output inductor constituted by the pipes 63 and 64, and the tuning condenser constituted by the vertical plates 24 and 25 and the rotary plates 31 and 32 carried by the vertical shaft 27, and since the median oint of the inductor is effectively grounded through the resistor 87 and the condenser 88, the said shaft is effectively at ground-potential in so far as radio-frequencies are concerned;

This is a valuable feature of our invention, inasmuch as the plate potentials used in devices of this character are often as high as 10,000 volts.

By reason of the fact that the capacity-ta ground of the several groups of thermionic devices is definitely fixed and not subject to variation because of the rigid structure and shields, minimum working constants may be used.

In addition, the extremely compact structure we provide'permits the use of interconnecting conductors of minimum length, and the amplifier unit may accordingly be so constructed that extremely high frequencies at Conversely, an adjustment of the several neutralizing condensers does not alter the tuning of the unit. The constancy of the capacity-to-ground of the amplifying unit follows from the fact that as the movable elements thereof rotate about vertical axes, the I adjusted.

The approximate equivalency of the capaclty, to ground of the several neutralizing condenser plates renders the process of neutralizingthe circuit against parasitic oscillations .far more rigidity than equivalent structures that were known to the prior art. Such rigidity is of minor importance in low-frequency amplifiers, but since, in the amplification of high-frequencies, relatively small capacities are required for tuningand neutralizing, the slightest variation in the spacing of the condenser-plates, resulting from extraneous vibrations, or from other causes, results in a relatively large variation in the amplitude ofthe outputf Our improved amplifier consetfllllelltly has a much more constant output t an previously constructed amplifiers for high frequencies at high powers.

Our improved amplifier structure is also compact, and is electrically so balanced that the neutralization thereof against parasitic oscillations'may be accomplished with minimum adjustment and, when once is effected, such neutralization is not disturbed by the operation of tuning.

Many other advantages of our invention will be apparent to those skilled in the art, as well as many modifications thereof in additionto those comprised in the specific embodimcnt thereof chosen for illustration. Our invention, therefore, is not to be limited except insofar as is necessitated by the prior art, or by the spirit of the appended claims.

We claim as our invention:

1. In combination, means adapted to sup-' port a thermionic device, and movable means electrostatically cooperating therewith to constitute a variable condenser.

2. In combination, means adapted to sup port a thermionic device, and a plurality of movable means electrostatically cooperating therewith to constitute tuning and neutralizing condensers.

3. In combination, means adapted to support a plurality of thermionic devices comprised in a balanced amplifier, movable means electrostatically cooperating therewith to constitute a tuning condenser, and movable means also electrostatically cooperating therewith toconstitute neutraliz ng condensers.

4. In combination, a'thermionic device of the power type having an external anode,

means adapted to support said device and to.

ort a thermionic device of the power type aving an external anode, said supporting means being arranged to make electrical con tact with said anode and to supply a-cooling medium thereto, and movable means electrostatically cooperating with said supporting means to constitute a variable condenser.

6. In combination, means adapted to support a plurality of thermionic devices of the power type having external anodes, said supporting means being arranged to make electrical contact with said anodes and to maintain a cooling medium in contact therewith, means for supplying a cooling medium to said supporting means, said last mentioned means also functioning as an inductor, and movable means cooperating electrostatically with said supporting means to constitute a tuning condenser electrically in shunt to said inductor.

7. In combination, means adapted to support a plurality of thermionic devices of the power type having external anodes, said supporting means being arranged to make electrical contact with said anodes and to maintain a cooling medium in contact therewith, means electrically connected to said supporting means to supply said cooling medium thereto, said supply means also functioning as an inductor, movable means cooperating electrostatically with said supporting means to constitute a tuning condenser, and a grounded shield positioned intermediate said movable means and said supply means, whereby the inductance of said supply means is unaffected by the adjustment of said movable means.

8. In combination, means adapted to support a plurality of thermionic devices and movable means electrostatically cooperating with said supporting means to constitute a variable capacity, said movable means being so positioned as to maintain substantially um orm capacity to ground, regardless of its position relative to the supporting means.

9. In combination, means adapted to support a thermionic device, an element located adjacent to, but spaced from, said support- I ing means, means for shifting the position pf said element with respect to said supporting means, said element comprising a substantially vertically positioned plate whereby a substantially uniform capacity to ground will be maintained, regardless of the position of said element with respect to said support.

10. In combination, a support, one portion of said support being electrostatically coupled to a movable means to constitutea variable capacity adapted for tuning pu oses and another portion of said support ing electrostatically coupled to another means to constitute a capacity adapted f0 neutral izing purposes, and a circuit embodying said support and associated capacities.

11. In combination, means adapted to supa uniform spacing between said supporting means and said spaced means is maintained.

In testimony whereof, we have hereunto subscribed our names this 13th day of Febru ary, 1928, and this 21st day of February, 1928,

respectively ROBERT L DAVIS DONALD G'. LITTLE. 

